Method for making multi-layer plastic preform for blow molding

ABSTRACT

A method for making a multi-layer plastic preform 14 with an inner layer 28 that is extrusion blow molded from a resin having an intrinsic viscosity greater than 0.90, and an outer layer 44 that is injection molded around the inner layer from a resin having an intrinsic viscosity that is at least 0.10 less than the intrinsic viscosity of the inner layer. The inner layer 28 is no greater than 200 (preferably no greater than 15%) by weight of the total weight of the preform and the outer layer 44 is at least 80% (preferably at least 85%) by weight of the total weight of the preform.

TECHNICAL FIELD

This invention relates to a multi-layer plastic preform for blow moldinga container and also relates to the method for making the preform.

BACKGROUND ART

Plastic blow molding of containers is conventionally performed either byextrusion of a hot plastic parison or by a plastic preform which isusually injection molded from plastic. The hot plastic parison or heatedpreform is received within a mold cavity whereupon pressurized gasprovides the blow molding of the container to the shape of the moldcavity.

With certain resins such as polyethylene terephthalate, the resin has tobe treated to increase its intrinsic viscosity in order to havesufficient strength to be extruded as a hot parison capable of beingblow molded, such as disclosed by U.S. Pat. No. 4,219,527 Etelman et al.Such processing of the resin increases its cost and hence the resultantcost to the consumer.

While preforms for plastic blow molding are conventionally injectionmolded from a single resin, there have also been prior multi-layerpreforms such as disclosed by U.S. Pat. Nos. 3,719,735 Valyi; 3,787,157Valyi; 4,067,944 Valyi; 4,391,861 Nilsson; and 4,646,925 Nohara.

Other prior art involving plastic resins, parison extrusion and preformsis disclosed by U.S. Pat. Nos. 4,398,642 Okudaira et al.; 4,564,541Taira et al.; 4,728,549 Shimizu et al.; 4,764,403 Ajmera; 4,816,308Shimizu et al.; 4,861,630 Mihalich; 4,874,647 Yatsu et al.; 4,994,313Shimizu et al.; 5,034,177 Niimi et al.; 5,039,780 Hashimoto et al.;5,115,047 Hashimoto et al.; 5,256,363 Hashimoto et al.; 5,281,387Collette et al.; 5,286,187 Niimi et al.; 5,380,479 Schrenk et al.; and5,439,718 Klerks et al.

DISCLOSURE OF INVENTION

An object of the present invention is to provide an improved method formaking a multi-layer plastic preform for blow molding a container.

The method for making a multi-layer plastic preform for blow molding acontainer in accordance with the above object is performed by extrudinga resin having an intrinsic viscosity greater than 0.90 as a parison ofa tubular shape. Blow molding of the parison is performed to provide aninner layer that is no greater than 20% by weight of the total weight ofthe preform. Thereafter, injection molding is performed with a resinhaving an intrinsic viscosity that is at least 0.10 less than theintrinsic viscosity of the inner layer to provide an outer layerextending around the inner layer and being at least 80% by weight of thetotal weight of the preform.

In the preferred practice of the method, the first mentioned resin isextruded and blow molded to provide a connected pair of preform innerlayers that are thereafter separated from each other in preparation forthe injector molding of the outer layer.

The preferred practice of the method is also performed by extrusion blowmolding of the inner layer from a resin having an intrinsic viscositygreater than 1.0 and by weight is less than 15% of the total weight ofthe preform, and the outer layer is injection molded from a resin havingan intrinsic viscosity that is at least 0.15 less than the intrinsicviscosity of the inner layer and by weight is at least 85% of the totalweight of the preform.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmode for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view taken through extrusion blow moldingapparatus for extruding a parison between open mold sections of a mold.

FIG. 2 is a view similar to FIG. 1 but showing the apparatus after themold has been closed to blow mold the extruded parison to provide a pairof preform inner layers.

FIG. 3 is a view illustrating how the pair of preform inner layers areseparated from each other.

FIG. 4 is a view that illustrates injection molding apparatus forinjection molding an outer layer around the inner layer to provide amulti-layer preform.

BEST MODE FOR CARRYING OUT THE INVENTION

The drawings illustrate extrusion apparatus 10 (FIGS. 1 and 2) andinjection molding apparatus 12 (FIG. 4) for making a multi-layer plasticpreform 14 for blow molding a container in accordance with theinvention. The construction of the preform 14 as shown in FIG. 4 and themethod for making the preform in accordance with the invention will bedescribed in an integrated manner to facilitate an understanding of thedifferent aspects of the invention.

With reference to FIG. 1 of the drawings, the extrusion apparatus 10includes an extruder 16 that extrudes a hot tubular parison 18 ofplastic resin between open mold sections 20 of an open blow mold 22. Theresin from which the parison 18 is extruded has an intrinsic viscositygreater than 0.90. The mold sections 20 of the blow mold 22 have cavitysections 24 that cooperatively define an enclosed cavity 26 upon closingof the mold 22 as shown in FIG. 2. The mold cavity 26 defines the shapeof a pair of inner layers 28 of the preform. One of the mold sections 20includes a blow needle 30 that is inserted into the parison 18 upon themold closing to blow mold the parison to the shape of the mold cavity 26in order to provide the pair of inner layers 28 that are connected attheir ends which are located adjacent the open ends of the resultantpreform after its injection molding as is hereinafter more fullydescribed.

After the extrusion and blow molding of the inner layers 28 asillustrated in FIG. 1, the mold 22 is opened to remove the connectedinner layers 28 which are then separated from each other in any suitablemanner such as by cutting by the schematically illustrated knives 32shown in FIG. 3.

With reference to FIG. 4, the injection molding apparatus 12 includes amold 34 having a pair of mold sections 36 that define mold cavitysections 38 for cooperatively defining a mold cavity 40 in the closedposition illustrated. The extruded inner layer 28 illustrated ispositioned on a core pin 42 of the injection molding apparatus 12 and isreceived within the cavity 40 of the closed mold 34 to commence theinjection molding processing. An injector 43 injects a resin into thecavity 40 about the inner layer 38 to provide an outer layer 44 of thepreform. The resin from which this injection molding is performed has anintrinsic viscosity that is at least 0.10 less than the intrinsicviscosity of the inner layer 28.

The multi-layer preform 14 has its inner layer 28 being no greater than20% by weight of the total weight of the preform 14 and has its outerlayer 44 being at least 80% by weight of the total weight of thepreform. This construction provides a preform that can be economicallyproduced and blow molded to provide a container that has good strengthcharacteristics at its base as a result of the inner layer with thegreater viscosity and consequent strength.

In the preferred construction, the inner layer 28 is extrusion blowmolded from a resin having an intrinsic viscosity greater than 1.0 andis no greater than 15% by weight of the total weight of the preform.Furthermore, the outer layer 44 is preferably injection molded from aresin having an intrinsic viscosity that is at least 0.15 less than theintrinsic viscosity of the inner layer 28, and the outer layer ispreferably at least 85% by weight of the total weight of the preform.

The construction of the multi-layer preform 14 can have the inner andouter layers 28 and 44 made of the same type of resin or of differenttypes of resin. Furthermore, the inner and outer layers 28 and 44 canboth be made of virgin resin. In addition, it is possible for the innerlayer 28 to be made of virgin resin and the outer layer 44 to be made ofpost consumer recycled resin. The inner layer 28 defines the entirety ofan interior surface of the preform 14, while the outer layer 44 definesthe entirety of an exterior surface of the preform. This constructionallows the inner layer 28 to be made of virgin resin that contacts thecontainer contents upon blow molding of the container, while the outerlayer 44 can be made of post-consumer recycled resin since it does notcontact the container contents.

While the best mode for carrying out the invention has been described indetail, those familiar with the art to which this invention relates willrecognize various alternative ways of practicing the invention asdefined by the following claims.

What is claimed is:
 1. A method for making a multi-layer plastic preformfor blow molding a container, comprising:extruding a resin having anintrinsic viscosity greater than 0.90 as a parison of a tubular shape;blow molding the parison to provide an inner layer that is no greaterthan 20% by weight of the total weight of the preform; and injectionmolding a resin having an intrinsic viscosity that is at least 0.10 lessthan the intrinsic viscosity of the inner layer as an outer layerextending around the inner layer and being at least 80% by weight of thetotal weight of the preform.
 2. A method for making a multi-layerplastic preform for blow molding a container as in claim 1 wherein thefirst mentioned resin is extruded and blow molded to provide a connectedpair of preform inner layers that are thereafter separated from eachother.
 3. A method for making a multi-layer plastic preform for blowmolding a container as in claim 1 wherein:the inner layer is extrusionblow molded from a resin having an intrinsic viscosity greater than 1.0and by weight is less than 15% of the total weight of the preform, andthe outer layer is injection molded from a resin having an intrinsicviscosity that is at least 0.15 less than the intrinsic viscosity of theinner layer and by weight is at least 85% of the total weight of thepreform.